Thermostat with stable switch mount

ABSTRACT

A line-voltage thermostat is described having a snap-switch proportioned to carry heavy line current to an electric room heater. The snap-switch is mounted on a baseplate which is to be mounted on a wall box. The screws used to mount the baseplate have long shanks so as to be accessible well forward of the baseplate. The mounting screws extend through arched straps which are sheared free of the baseplate except at their ends. This avoids upset of the calibration due to deformation of the baseplate during tightening of the mounting screws, considering mainly the area of the baseplate where the switch is mounted. The thermostat has a bimetal held at a hinge point by a single unique spring. Fixed ears project toward the bimetal to limit the extent the bimetal can be depressed, protecting the switch from damage and from calibration error due to excessive manual force on the bimetal when the thermostat is being installed or serviced.

. United States Patent [72] Inventors Jean R. Fortier 3,454,919 7/ i969Kulick 337/360 south o'mget Primary Examiner-Bernard A. Gilheany Paul M-Moskowltz, Brooklyn, N-Y. Asst-am p B Be [2]] App]. No. 83,994Ar'tomeyPaul S. Martin [22] Filed Oct. 26,1970 V [45] Patented Dec.21,1971 [73] As gn" Fedfl'll Plcmc Ekfll'lc l y ABSTRACT: A line-voltagethermostat is described having a NW 'h -J' snap-switch proportioned tocarry heavy line current to an electric room heater. The snap-switch ismounted on a baseplate which is to be mounted on a wall box. The screws[54] THERM-OSI'EAT r g, STABLE SWITC MOUNT used to mount the baseplatehave long shanks so as to be ac- 4 Claims cessible well forward of thebaseplate. The mounting screws [52] U.S.Cl 337/333, extend througharched straps which are sheared free of the 337/338, 337/360, 337/372,337/380, 337/417 'baseplate except at their ends. This avoids upsetofthe calibra- [51] Int. Cl. l-l0lh 37/52 tion due to deformation of thebaseplate during tightening of [50] Field of Search 337/42, the mountingscrews, considering mainly the area of the 102, 111, 333, 334, 338, 360,363, 372, 379, 380, baseplate where the switch is mounted.

417, 337 The thermostat has a bimetal held at a hinge point by a singleunique spring. Fixed ears project toward the bimetal to 1 kekl'mc's Cnedlimit the extent the bimetal can be depressed, protecting the UNITEDSTATES PATENTS switch from damage and from calibration error due toexces- 2,171,272 3/1939 m et a 337 3 sive manual force on the bimetalwhen the thermostat is being I installed or serviced. 74mm A 4 W 45 7% fd /0- A I Z i 26 A, *I L 4x 52 .772 if Tag-fa w if 7a 3% We 52 .wii 4% ll8 mounted on the same base-plate as the one which carries the mountingscrews for securing the thermostat to the junction box. Any deformationof the thermostat base-plate caused by the mounting screws may upset thecalibration. A feature of the present invention involves locating themounting screw holes in respective arched strips that arestress-isolated from the area of the base plate that carries the switch.The strips are provided at each of the ends of the base plate, and theyextend from opposite corners of the flanged base-plate. In contrast tomany other configurations, this mounting-strap feature has been foundextremely effective in divorcing distortions produced in the mountingstructure by the tightened mounting screws from disturbing theswitch-mounting area, thus making the thermostat calibration highlyimmune to mounting stresses.

The presently described thermostat involves a secondary plate acting asa heat shield betweenand spaced from-the bimetallic sheet and the mainbase-plate of the thermostat. In use, this main plate is secured bymounting screws to a wall box. The mounting screws have bearingshoulders against the mounting strips of the main base plate. Thesescrews have upstanding stems that are slotted for screw-driveroperation, and the stems project well forward of the main base plate.This feature makes the screws easily accessible to the installer, andthereby protects the bimetallic sheet in front of the subplate fromdamage that might be caused inadvertently by the installer in gropingfor deeply recessed mounting screws.

The nature of the invention will be more fully appreciated from thefollowing detailed description of an illustrative embodiment of theinvention shown in the accompanying drawings. In the drawings:

FIG. 1 is a central vertical cross section perpendicular to the front ofan illustrative thermostat embodying the features of the invention;

FIG. 2 is front view of the thermostat of FIG. I with the cover andother parts in front of the bimetal removed, certain partly removedparts being shown in cross section; and a portion of the bimetal beingbroken away;

FIG. 3 is a rear view of the thermostat as in FIG. 2, part of the switchbeing broken away to expose detail of the base plate;

FIG. 4 is a horizontal cross section of the thermostat of FIGS. 1-3looking upward from the plane 44 of FIG. 3;

FIG. 5 is an enlarged detail of FIG. 1;

FIG. 6 is a bottom view of the thermostat base plate; and

FIG. 7 is a perspective view ofa spring in FIGS. l-3.

Referring now to the drawings, a wall box B is suitably supported in anopening in wall W. The thermostat has a main mounting plate 10 havingside flanges l2 and top and bottom flanges 14 which provide stiffeningand which space the central area 16 away from wall W. Arched mountingstraps l8 and 20 extend integrally from top and bottom flanges l4 andinitially are in the plane of flat central area 16. The edges of thesestraps are cut clean and do not bind or interlock with the adjoiningmetal. I-Iorizontal'and vertical slots 22 and 24 are provided in strapsl8 and 20 for screws 26. Each of these screws has a laterally projectingshoulder or flange 28 overlying strap 18 (20), a fiber washer 30 behindthe strap that holds the screw captive, and an elongated stem 32 thathas a screwdriver slot at its upper end.

A switch 34 is screwed to area 16 at the rear of the main mounting plateso as to be received in box B. Short posts 34a extend integrally fromswitch 34 at each of the mounting points, providing an air space betweenarea 16 of main mounting plate 10 and switch 34.

Holes or slots 38 in flanges l4 are provided for admitting anddischarging convection air currents, for carrying away heat generated inswitch 34. These slots do not extend to the extremities of straps I8 and20 so that those straps are integral with relatively strong portions offlanges 14.

A secondary plate 40 is secured to main mounting plate I0 by four screws42 in area 16. These screws extend from the rear of plate 10 throughspacing sleeves 44 that are of plastic, ceramic or other solid thermalinsulation. The space between plates 10 and 40 is a second convectionair space for carrying away any heat that was developed originally inthe switch and that reached plate 10 in some small degree. Secondaryplate 40 has sidewalls 40a along its vertical margins. At the bottom,each sidewall 40a is bent at right angles to form arms 40b; andbimetal-locating lugs 40c extend from these arms 40b. Arms 40b form ahinge or fulcrum across ambient temperature sensing bimetal 46 near itsbottom edge. Lugs 40c extend through a pair of holes 460 in the bimetal.A biasing spring 48 (FIG. 7) has a very wide V-shaped central portion48a that is received at its apex in a slot 40d. Spring 48 hasreverse-bent portions or hooks 48b extending about the upper and lowersides of lugs 40c. bearing against the side of bimetal 46 that facesplate 40. Slot 40d is transverse to plate 40 and is aligned with ears40c. Spring 48 is of wire that is nearly as thick as slot 40d is wide.Because of the fit of spring part 48a in slot 40d, part of spring 48near its extremity at the left as viewed in FIG. 2 bears against thebottom face of one lug 40c and part of the spring near its right-handextremity bears against the top face of the other lug 400. The overalleffect of this configuration is to provide dependable pressure of thespring against bimetal 46, a pressure that remains consistent among manythermostats and mechanically stable in each thermostat. The smallmovement that may be exerted on the bimetal by one end of the springacting about the pivot represented by the related arm 40b is canceled bya like opposite movement at the other arm 40b.

Remote from the lower hinged end of the bimetal, near the top of thebimetal, there is a cam-follower in the form of a button 50 securedrigidly to the bimetal. A cam 52-is supported on a rotatable shaft 54for cooperation with cam-follower 50. A reduced end portion 54a of shaft54 extends through a hole in secondary plate 40. The shoulder formed bythe largediameter portion of shaft 54 at the front of plate 40 forms astable bearing surface against plate 40. Small diameter portion 54aextends through plate 40. Shaft 54a is held in assembly to plate 40 by aspecial washer 56 that is force-fitted over shaft extension 54a to bearagainst a further washer 58 at the back of secondary plate 40.

Switch 34 in the form illustrated, is a double pole switch, having twoseparate switching parts of the so-called microswitch or overcenteringsnap-switch variety. The switch is in a normal" stable configurationwhen its rod 34b is released, and the switch is operated" or moved outof its normal" position when rod 34b is pushed deeper into the switchbody. For each pole of the switch, a set screw 60 is provided in bimetal46 and cooperates with the end of rod 34b remote from switch 34. Thisrod extends through oversize holes in plates 10 and 40, and is guided bya bushing 34c of the switch. The switch biases rod 34b outward, so thatrod 34b normally biases its set screw 60 toward the left (FIG. I) andaway from the switch. This effect causes button 50 to bear against cam52. When the bimetal is subjected to a rising ambient temperature, itscenter portion becomes arched toward the right as viewed in FIG. Icausing rod 34b to reverse the condition of switch 34 from normal" toits operated condition. Screw 60 is used to provide for calibration, andcam 52 enables the user to adjust the set point of the thermostat. Cam52 has an extreme position or portion (not shown) which coacts withcam-follower 62 for deflecting bimetal 46 to the right in such a way asto insure operation of both poles of switch 34 out of their normalcondition for even the lowest temperature to be experienced by thethermostat. Cam 52 represents a conventional off operator for both polesof the switch. Various combinations of switches are used in variousthermostats, sometimes including a snap switch at one pole and aslow-acting switch operated by cam-follower 62 as the other pole. Atother times, both poles of the switch are snap switches and are arrangedto operate at or nearly at the same set-point.

A transparent cover 64 encloses that portion of the thermostatcontaining bimetal 46. Slots 640 at the top and bottom provides forconvection air currents entering the cover and moving along the frontand back of bimetal 46. Knob 66 fixed to shaft 54 operates cam 52. Anedge portion of knob 66 extends laterally through a slot (not shown) incover 64 for changing the set-point of the thermostat, A cover plate 68has lateral lugs that are received in retaining slots 69, one such slotbeing provided in each sidewall 40a near the bottom thereof and anothersuch slot being provided in each sidewall 40a near the top thereof forreceiving lateral lugs of plate 68. All slots 69 open upward, so thatplate 68 slides down into the slots, when the plate is being mounted.Cam 52 is received in an oversized hole in plate 68.

A so-called anticipator resistor 70 is held against bimetal 46 by aretaining clip 72 that is riveted to the bimetal. Flexible insulatedconnecting wires 700 from resistor 70 extend through drawn holes 74 and76 in plates 40 and 10, respectively. The anticipator wires extend tothe rear of plate where suitable electrical connections are made,customarily to the load-side terminals of the two poles of switch 34.

In mounting the thermostat, cover 64 is snapped off the ends of plate40, knob 66 is removed and plate 68 is slid upward and removed. At thetop of the thermostat, slotted stem 32 of one screw 26 is easily engagedfor operation because it extends well forward of plate 40, through anoversized hole in that plate. Near the bottom of the thermostat, thereis an opening 46b, and stem 32 of the lower screw 26 extends to aconvenient level close to the plane of the bimetal for easy access andoperation. Screws 26 are therefore easily operable from the front of thethermostat, and they drive their respective straps l8 and 20 .firmlybackward (and against) the mounting ears of box B. Despite theconsiderable deformation of straps l8 and 20 that is possible, area 16is not warped or distorted in this operation. Consequently therelationship of screw(s) 60 and switch rods 34b which is criticallyadjusted at the factory in a calibration operation, is not disturbed.

A pair of stops 78 extend forward as integral parts of secondary plate40. Stops 78 resist positively any deflection of bimetal 46 beyond acertain point. In the absence of such stops 78, careless pressureapplied to bimetal 46 could drive rods 34b too far into the body ofswitch 34, possibly causing permanent deformation or other damage to theswitch. This might not disable the switch, but the thermostatcalibration could be upset.

We claim:

1. A thermostat including a base plate having a switchmounting area, abimetallic sheet disposed generally parallel to said switch-mountingarea, a switch mounted on said base plate in said area, means forming acalibrated coupling between said switch and said bimetallic sheet, andmounting straps at opposite ends of the base plate, the extremities ofeach mounting strap extending integrally from margins of the base plateat the opposite ends thereof, each of said straps having an aperturespaced from said extremities for receiving a mounting screw to securethe thermostat to a wall box without deforming said switch mountingarea,

2. A thermostat in accordance with claim 1, including a secondary platebetween the bimetallic sheet and the base plate and separated byrespective air spaces therefrom, and respective screws in saidapertures, each of said screws having a shoulder bearing against therelated strap and having a screwdriver-slotted stern projecting wellforward of said base plate.

3. A thermostat in accordance with claim 1, wherein said straps arecurved toward each other so as to dispose said screw-receiving aperturessubstantially inward from the opposite-end margins of said base plate 4A thermostat in accordance with clam; 1, wherein said base plate is arectangular metal sheet having marginal flanges, and wherein said strapsextend substantially form the comers thereof.

1. A thermostat including a base plate having a switch-mounting area, abimetallic sheet disposed generally parallel to said switch-mountingarea, a switch mounted on said base plate in said area, means forming acalibrated coupling between said switch and said bimetallic sheet, andmounting straps at opposite ends of the base plate, the extremities ofeach mounting strap extending integrally from margins of the base plateat the opposite ends thereof, each of said straps having an aperturespaced from said extremities for receiving a mounting screw to securethe thermostat to a wall box without deforming said switch mountingarea.
 2. A thermostat in accordance with claim 1, including a secondaryplate between the bimetallic sheet and the base plate and separated byrespective air spaces therefrom, and respective screws in saidapertures, each of said screws having a shoulder bearing against therelated strap and having a screwdriver-slotted stem projecting wellforward of said base plate.
 3. A thermostat in accordance with claim 1,wherein said straps are curved toward each other so as to dispose saidscrew-receiving apertures substantially inward from the opposite-endmargins of said base plate.
 4. A thermostat in accordance with claim 1,wherein said base plate is a rectangular metal sheet having marginalflanges, and wherein said straps extend substantially form the cornersthereof.